The present invention relates to a radio wave absorbent for use in an anechoic chamber, a radio wave absorbent-assembling member which can be used in the radio wave absorbent, and a method for producing the radio wave absorbent.
Recently, the use of a radio wave has been rapidly extended, mainly in the mobile information field, toward realizing highly developed information society. Further, with the great progress of recent microelectronics technique, various electric apparatus have been spread. However, with such a progress of information communication technique, the influence of unnecessary electromagnetic noises exerted onto precision apparatus associated devices has posed problems.
For the measurements of electromagnetic noises, an anechoic chamber where there is no reflection of electromagnetic waves is generally used, and a radio wave absorbent is arranged in the inner wall of the anechoic chamber. As the conventional radio wave absorbent used in the anechoic chamber, there can be mentioned one that is composed of an organic material, such as a foamed polystyrol, a foamed polystyrene or a foamed polyurethane, which has incorporated thereinto carbon black or the like for obtaining a conductivity. In addition, the radio wave absorbent is used as a stereo-structure in the form of quadrangular pyramid, triangular prism or wedge. Such a radio wave absorbent as a stereo-structure is generally produced by, for example, a method in which particles of an organic material, such as polystyrol, polystyrene or polyurethane without foaming, are prefoamed into spheres having a diameter of several mm, and the surfaces of the spheres are coated with a conductive material powder, such as carbon black, followed by heating in a desired die, to thereby effect post-foaming.
Further, in recent years, there have been proposed a member for a radio wave absorbent which is a stereo-structure having a hollow inner portion, and the method for producing the radio wave absorbent (see Japanese Patent No. 2760578 and Japanese Patent Application Laid-Open Specification Nos. 67544/1996, 275295/1997, 307268/1997 and 163670/1998).
However, the radio wave absorbents in the form of quadrangular pyramid, triangular prism, wedge and the like produced by the method in which an organic material, such as polystyrol, polystyrene or polyurethane, is heat-foamed as mentioned above have problems in that not only is the carrying of the radio wave absorbent difficult during the construction of an anechoic chamber since the radio wave absorbent is bulky, but also the radio wave absorbent is damageable against contacting and the like.
Further, in the production method described in Japanese Patent No. 2760578, a treatment in which a predetermined portion for folding is locally heated and softened is needed. Therefore, a problem arises in that the operation is complicated. In addition, a thermoplastic synthetic resin is used in a radio wave absorbent in this method. Therefore, when such a radio wave absorbent is used in the anechoic chamber for a test using a large electric power, such as immunity test, the radio wave absorbent has problems from the viewpoint of safety because it has poor non-combustibility and poor fire resistance.
Further, in the member for a radio wave absorbent and the method for producing the same described in Japanese Patent Application Laid-Open Specification No. 67544/1996, a radio wave absorbent in which a lightweight mortar is used has been proposed. However, in this prior art technique, it is necessary to employ a plurality of treatment steps as well as a plurality of members. Therefore, a problem arises in that the operation is complicated. In addition, organic hollow particles and organic binders, which are used in large amounts and used for reducing the weight of the mortar, are semi-non-combustible materials. Therefore, there is a problem in that the smoking amount is extremely large, as compared with that expected in the case using a non-combustible material.
Further, the radio wave absorbent described in Japanese Patent Application Laid-Open Specification No. 275295/1997 has a problem of a very high production cost.
Further, in the radio wave absorbent described in Japanese Patent Application Laid-Open Specification No. 307268/1997, not only a molded material made of a ceramic fiber and a glass fiber but also a plurality of production steps are needed. Therefore, there is a problem in that the production cost is high.
Further, with respect to any of the above-mentioned conventional radio wave absorbents having a hollow stereo-structure, the weight reduction is not satisfactory. Therefore, there is a problem in that the workability is poor when the radio wave absorbent is installed in the sidewall and the inner wall of the ceiling of the anechoic chamber.
In view of the above, the present invention has been made, and an object of the present invention is to provide a radio wave absorbent which is advantageous not only in that the workability is excellent during the construction of an anechoic chamber, but also in that it has a non-combustibility and a desired form, a production method which is advantageous in that the above radio wave absorbent can be easily produced, and a radio wave absorbent-assembling member which can be used for the above radio wave absorbent.
For attaining the above object, the radio wave absorbent-assembling member of the present invention has a construction such that it comprises a radio wave absorptive thin material capable of assembling a structure in a desired form, wherein the thin material contains a conductive material therein and/or has on the surface thereof a conductive layer containing a conductive material.
The radio wave absorbent of the present invention is formed using a radio wave absorbent-assembling member and has a construction such that it is a structure formed by folding the radio wave absorbent-assembling member which comprises a radio wave absorptive thin material capable of assembling a structure in a desired form and joining together the end portions of the folded radio wave absorbent-assembling member, wherein the thin material contains a conductive material therein and/or has on the surface thereof a conductive layer containing a conductive material.
The method for producing a radio wave absorbent of the present invention comprises: processing a thin material into a form which is capable of assembling a structure in a desired form, to thereby prepare a radio wave absorbent-assembling member, wherein the thin material contains a conductive material therein and/or has on the surface thereof a conductive layer containing a conductive material; and folding the radio wave absorbent-assembling member and joining together the end portions of the folded radio wave absorbent-assembling member.
The present invention is advantageous not only in that it is possible to reduce both of the weight of a radio wave absorbent and the production cost thereof since the radio wave absorbent-assembling member is made of a radio wave absorptive thin material, but also in that the carrying or the like of the radio wave absorbent-assembling member is very easy during the construction of an anechoic chamber since the radio wave absorbent-assembling member is in a plane form and not bulky. Further, by the present invention, a radio wave absorbent can be produced simply by folding a radio wave absorbent-assembling member into a structure in a desired form without any pretreatment of the radio wave absorbent-assembling member. Therefore, the workability is extremely excellent, and the radio wave absorbent obtained by using a non-combustible paper as a thin material has a non-combustibility. In addition, when a frame member is fixed to a unit comprising a plurality of radio wave absorbents, the installation of the radio wave absorbents to the inner wall of an anechoic chamber can be performed unit by unit. Therefore, the workability during the construction of the anechoic chamber can be remarkably improved. Further, after installation of the radio wave absorbent of the present invention, the safety with respect to the accidents, such as contacting, is extremely excellent, and when the radio wave absorbent suffers a damage, an exchanging or repairing operation is easy since the cost for the radio wave absorbent is low and the workability including an installation is excellent as mentioned above. In addition, since a non-combustible paper is used as a thin material, it is possible to destroy the radio wave absorbent simply by folding compactly. Therefore, the workability is excellent, and the radio wave absorbent can also be recycled.